Electronic assembly having cooling means for stacked modules

ABSTRACT

A modular electronic system includes a plurality of stacked electronic units. The stacked units have a first cavity therethrough along one edge thereof, and a second cavity therethrough along an opposite edge thereof. Each of the units has a spacing joining the two cavities. A first mounting plate has an orifice therethrough for communicating with the first cavity, and a second mounting plate has an orifice therethrough for communicating with the second cavity. Means are provided for clamping the fist mounting plate, the stacked units, and the second mounting plate together, so that cooling fluid can be passed from an exterior source through the first mounting plate orifice, through the first cavity, through in parallel all of the spacings, through the second cavity, and exiting through the second mounting plate orifice.

United States Patent Rathjen et al.

' [22] Filed:

[54] ELECTRONIC ASSEMBLY HAVING COOLING MEANS FOR STACKED MODULES [72]Inventors: J. Fred Rathien, Franklin Lakes; Lothar Laermer, Paramus,both of NJ [73] Assignee: The Singer Company, New York, NY.

Oct. 22, 1970 [21] Appl. No.: 82,873

[52] US. Cl "317/100, 174/15 R, 317/101 CM [51] Int. Cl. ..H05k 7/20[58] FieldofSearch ..l74/l5R,16R,16l-1S;

317/100, 101 DH, 101 CM, 101 CX [56] References Cited UNITED STATESPATENTS 6/1960 Woodward ..3l7/100X 3/1964 Green "317/100 Mar. 7, 19723,395,318 6/1968 Laemer ..3l7/l00 Primary Examiner-Lewis H. MyersAssistant Examiner-Gerald P. Tolin Attorney-S. A. Giarratana and ThomasW. Kennedy [5 7] ABSTRACT A modular electronic system includes aplurality of stacked electronic units. The stacked units have a firstcavity therethrough along one edge thereof, and a second cavitytherethrough along an opposite edge thereof. Each of the units has aspacing joining the two cavities. A first mounting plate has an orificetherethrough for communicating with the first cavity, and a secondmounting plate has an orifice "therethrough for communicating with thesecond cavity.

Means are provided for clamping the fist mounting plate, the stackedunits, and the second mounting plate together, so that cooling fluid canbe passed from an exterior source through the first mounting plateorifice, through the first cavity, through in parallel all of thespacings, through the second cavity, and exiting through the secondmounting plate orifice.

7 Claims, 7 Drawing figures Patented March 7, 1972 3 Sheets-Sheet l 2m;fifilv AX /M WM W Ix m W W a g Q J. a WWW 5:====RWHEEE=======t- M I 6 Wm m Patented March 7, 1972 3 Sheets-Sheet 2 \FFT Zi I ZZ'Z-Zi INVENTORS.1 Fred Ram en BY LofharLaermer MUM"! riauzi Patented March 7, 1972 3Sheets-Sheet a unr nee mm vae NR d Eullip-IE! ELECTRONIC ASSEMBLY HAVINGCOOLING MEANS FOR STACKED MODULES BACKGROUND OF THE INVENTION Thisinvention relates to modular electronic systems and, in particular,relates to a high-density electronic packaging arrangement whichprovides for efficient heat dissipation and can withstand high vibrationand shock. Accordingly, the general objects of the invention are toprovide new and improved apparatus of such character.

Various electronic packages have been designed in the past with variousdegrees of effectiveness for housing electronic components andfordissipating the heat generated thereby.

In the U8. Pat. No. 3,395,3l8, issued July 30, 1968 to Lothar Laermer(one of the applicants hereof) and Arthur J. Pretty and Philip Gray andassigned to the assignee of this invention, a circuit board cardarrangement for the interconnection of electronic components isdescribed. The aforesaid patent relates to a circuit board for theinterconnection of electronic components such as flat packs and discretecomponents, and includes a flat rectangular plate with an insulatingcoating having a plurality of apertures wherever necessary for passingleads. Around the plate is a metal frame and an extension which may becoupled to a heat exchanger. Over one or both faces of each flat side ofthe plate is an epoxy resin and an XY circuit board with X-lines on oneside and Y-lines on the other. Electrostatic shielding is provided byapplying a ground termination to the plate.

Apparatus, constructed and operated in accordance with the teachings ofthe aforementioned patent, utilized a plurality of card units in whicheach card unit contained a central aluminum core and two epoxy circuitboards laminated to each side of the core. The aluminum body of eachcard unit was connected by contacts to the outside surface of a frame.The outside surface of the frame was formed in a corrugated manner toact as a heat exchanger so that, when air was blown past the outsidesurface of the frame, the large corrugated surface area would give upheat to effectively cool the entire electrical package. Air would bepassed from one card, to the next card, and to the succeeding cards in amanner which could be referred to as a series type heat exchanger. Withsuch a system (as a series-type heat exchanger), when air is blown fromone side to the opposite side, by the time the air gets to the oppositeside, the air would be hot and insufficient cooling might take place atthe rear of the unit. Hence, such an electronic package is limited tocomparatively low-wattage ratings per card, for example, to about 3watts of power per card. Disadvantageously, however, such a system doesnot work well in dealing with higher wattages, for example, in the orderof watts per card.

At the bottom of such apparatus, an integral, interconnect board,otherwise termed a motherboard, contained all the interconnectconnections in one solid block for all the modular circuit board units.Disadvantageously, the motherboard was fixed dimensionally, was noteasily changeable, and would necessitate a redesign if it was desiredthat additional circuit boards be added to the overall system.

ln prior systems, flat printer circuit pins or male contacts wereoriented and aligned with the flat surfaces of the pins parallel to thesurface of the board. Each card was individually retained in themotherboard by corresponding female contacts.

It is desired to provide an electrical system which occupies as minimuma volume as possible. When electrical circuitry is placed into a housingwhich is close quartered so as to utilize a small volume, a heat problemarises. Thus, it is desired to provide for efficient dissipation of theheat. In addition, in complex electronic circuits, such as computers, itis desired to make the system expandable. Also, it is desired to providea system which is able to withstand high shock and vibrations for ruggedcommercial or government applications.

SUMMARY-OF THE'INVENTION Another object of this invention is to providenew and improved modular electronic systems.

It is another object of this invention to provide new and improvedmodular electronic systems in which the thermal resistance between thesource of heat and airflow passing by the heat exchanger is less thancorresponding designs of the prior art.

Another object of this invention is to provide new and improved modularelectronic systems which can withstand high shock and vibration.

Still another object of this invention is to provide new and improvedmodular electronic systems in which the systems can be made expandableby adding additional components thereto or by deleting severalcomponents therefrom, without necessitating a complete redesign of sucha structure.

With these and other objects in mind, a modular electronic system can beprovided including a plurality of stacked electronic circuit unitshaving a first cavity through the stack along one edge thereof and asecond cavity through the stack along an opposite edge thereof. Each ofthe units has a spacing joining the two cavities. A first mounting plateis provided having an orifice therethrough for communicating with thefirst cavity. A second mounting plate has an orifice therethrough forcommunicating with the second cavity. Means are provided for clampingthe first mounting plate, the stacked units, and the second mountingplate together so that cooling fluid can be passed from an exteriorsource through the first mounting plate orifice, through the firstcavity, through in parallel all of the spacings, through the secondcavity, and exiting through the second mounting plate orifice.

More specifically, the invention contemplates a modular electronicsystem including a first plurality of stacked electronic circuit unitswherein each of the units includes a first laminate formed by a firstsubstantially rectangular printed circuit board having componentsthereon, a first substantially rectangular thin sheet of heat conductivematerial, and insulating means for laminating the printed circuit boardto the printed sheet. The unit further includes a second laminatesimilarly formed. A hollow heat conductive frame holds the twolaminates, one on each side thereof, wherein the sheets of bothlaminates are oriented inwardly with respect to the frame and separatedfrom each other to form a spacing between them, the frame being formedin a generally rectangular configuration having four border members. Afirst elongated aperture is formed through and along one of said bordermembers from one side of the frame to the opposite side thereof. A slotis provided joining the first elongated aperture to the spacing.Similarly, a second of the border members nonadjacent to the firstmember has an elongated aperture formed therethrough and therealong fromone side of the frame to the opposite side thereof, and further having aslot joining the second elongated aperture to the spacing. The laminatesare fixed to both sides of the frame. The modular electronic systemfurther includes a front mounting plate in contact with one end of thestacked electronic units having an orifice therethrough forcommunicating with the first elongated apertures of the frames, and aback mounting plate in contact with the opposite end of the stackedelectronic units having an orifice therethrough for communicating withthe second elongated apertures of the frames. The front and backmounting plates the the intermediately oriented stacked electronic unitsare clamped so that cooling fluid can be passed from an outside source,serially through the front mounting plate orifice, through a plenumformed by the stacked first elongated apertures of the circuit units,through in parallel the first slots of all the frames, then the spacingof all the frames, thereby directly cooling the sheets and indirectlycooling the boards and the components on the boards, and then the secondslots of all the frames, serially through a cavity formed by the stackedelongated apertures of the circuit units, and exiting through the backmounting plate orifice.

In certain features of the invention, the printed circuit boards havemale electrical contacts disposed along a third of the border membersand further include electrical interconnecting means including femaleelectrical contacts for mating with the male contacts. Each maleelectrical contact has a width substantially greater than its thicknessand is so oriented with its width perpendicular to the surface of theprinted circuit boards. The corresponding mating female electricalcontacts are tight fitting with respect to thickness and loose fittingwith respect to width.

Additional features of the invention include electrical interconnectingmeans having a first electrical interconnect board containing femaleelectrical contacts for communicating with the corresponding malecontacts of the first plurality of the adjacent stacked electroniccircuit units, a second electrical interconnect board containing femaleelectrical contacts for communicating with corresponding male contactsof a second plurality of adjacent stacked electronic units and flexibleelectrical wiring tape for joining the first interconnect board to thesecond interconnect board. The modular system would further include adummy electronic circuit unit having a plate having an elongatedaperture along two opposite borders thereof so as to align, plenum andcavity, with the first and second pluralities of stacked units, saidplate having a concavity within the third border thereof, so as toreceive a loop ofthe tape therewithin. The wiring tape would have alength exceeding a value L +T wherein L is a value representing thewidth of the dummy plate and wherein T is a value representing themaximum dimensional tolerance error in width that could occur bystacking a first plurality of adjacent stacked circuit units together.

In an additional feature of the invention, each of the stackedelectronic circuit units contains a heat conductive structural memberjoining one of the border members intermediate the first elongatedaperture to the second of the border members intermediate the secondelongated aperture. The width of the various structural members areoptimized so as to vary the cross-sectional area of the spacings of eachunit and to control the corresponding coolant fluid flow ratetherebetween so as to optimize the degree of cooling ofeach circuitunit.

BRIEF DESCRIPTION OF THE DRAWING Other objects, advantages, and aspectsof the invention will become apparent by reference to the followingdetailed specification and drawings of a specific embodiment thereof,wherein:

FIG. 1 is a perspective view of one embodiment of the invention;

FIG. 2 is a sectional view taken along the lines 2-2 of FIG.

FIG. 3 is a sectional view taken along the lines 3-3 of FIG.

FIG. 4 is a sectional view taken along the lines 4-4 of FIG.

FIG. 5 is a schematic plan view showing the flow of cooling fluidthrough the system illustrated in FIG. 1;

FIG. 6 is an exploded view of an electronic circuit unit for use in theembodiment of FIG. 1; and

FIG. 7 is a partial cross-sectional view of an electronic circuit unitincluding a discrete component, such as a resistor, affixed to one sideof the unit in which the leads of the components are coupled to theopposite side of the unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates, inperspective, a modular electronic system 10 constructed in accordancewith the teachings of this invention. The system 10 includes a pluralityof stacked electronic units 11-11, one of the units 11 being shownpartially removed from the stack to provide for a better understandingof the invention. An optional, enclosing cover 12 is shown partly brokenaway and exploded away from the unit 10 to provide for a betterpictorial representation of the view. The

21-21 at its four corners so as to receive the two upper cover 12 is notnecessary for an understanding of the invention.

A front mounting plate 13 has an orifice 14 for an air inlettherethrough for providing a coolant fluid through to the system 10. Thecoolant fluid may be air or other suitable medium. The front mountingplate 13 includes various electrical connectors 16-16 for mating withelectrical cables (not shown) for connection to other electricalapparatus (not shown). A rear mounting plate 18 is provided at theopposite end of the system 10. Clamping arms 19-19, at both the upperleft and upper right of the system 10, are pivotally connected to therear mounting plate 18, and are adapted to engage with the frontmounting plate 13 so as to clamp the rear mounting plate 18, all of theelectronic units 11-11, and the front mounting plate 13 together in astacked arrangement. The clamping arms hold the units 11-11 togetherfrom front to back. They do not press the units ll-ll down as such. The

units 11-11 form an integral part of a boxlike structure so thatvibration is kept to a minimum.

FIG. 2 shows a sectional view of an electronic unit 11 taken along thelines 2-2 of FIG. 1. FIG. 6 illustrates an exploded view thereof. Theelectronic unit 11 includes a hollow, heat conductive frame 20constructed of suitable heat conductive material, such as aluminum. Thehollow frame 20 is generally rectangular in shape and is provided withcutaway notches clamping arms 19-19 and lower guide rods (not shown).The hollow frame 20 is formed with a left border member 22, a top bordermember 23, a right border member 24, and a lower border member 25. Theleft border member 22 has an elongated aperture 27 formed therein andtherealong from one side of the frame 20 to the opposite side thereof.Similarly, the right border member 24 contains an elongated aperture 28therethrough and therealong from one side of the frame 20 to theopposite side thereof.

A slot 29 joins the aperture 27 to the interior or hollow portion of theframe 20. The slot 29 may be constructed of two distinct slot portions29a, 29b between the aperture 27 and the hollow portion of the frame 20.The slot portions 29a, 2912 can be separated by a structural member 31which joins the left border member 22 to the right border member 24. Insimilar fashion, slot portions 32a, 32b join the hollow portion of theframe 20 to the aperture 28 of the right border member 24.

Most of the units 11-11 include the structural member 31, or centralspacer from one side to the other to provide support. The width of themember 31 can vary, depending upon the amount of air in which is desiredto flow through the unit 11 to provide for optimum heat dissipationtherethrough.

The electronic unit 11 includes the hollow heat conductive frame 20 asits basic structural member. In addition, the unit 11 includes a pair oflaminates 36, 43 (FIG. 6), one affixed to each side of the frame 20. Thelaminate 36 includes a first, substantially rectangular printed circuitboard 33, having components 34-34 disposed thereon, and a first,similarly shaped rectangular thin sheet 35 of heat conductive metal,such as copper. Electrical insulating means 37 are provided forlaminating the printed circuit board 33 to the metal sheet 35. In asimilar fashion, a second printer circuit board 39, a metal sheet 41,and electrical insulating means 42 are laminated together to form thelaminate 43. The laminates 36 and 43 are affixed to each side of theheat conductive frame 20 by means of adhesive 44.

When the laminates 36 and 43 affixed to both sides of the hollow frame20, suitable electrical connections are provided for coupling theprinted circuit boards 33 and 39 through the lower border member 25 ofthe frame 20, in a manner depicted in FIG. 2.

FIG. 2 further illustrates the electronic unit 11 inserted into anelectrical connection medium, such as a motherboard 50, through the useof male electrical contacts 51-51.

The male electrical contacts 51-51 of the printed circuit boards 33, 39fit within corresponding female electrical contacts of the motherboard50. Each male electrical contact 51 has a width substantially greaterthan its thickness. The contacts 51-51 are so oriented with their widthsperpendicular to the surface of the printed circuit boards 33, 39. Themating female electrical contacts of the motherboard 50 are tightfitting with respect to thickness and loose fitting with respect towidth, so that the electronic units 11-11 can be slightly moved in adirecting towards or away from the front of the system as showninFlG. 1. The contacts 51-51 of the printed circuit boards 33, 39 areoriented perpendicular to the surfaces thereof so that when they are fedinto the motherboard 50, they may move longitudinally to permit for somemovement with respect to the motherboard due to tolerance accumulations.Hence, by putting in a number of units 11 (eg, eight units) into amotherboard, due to tolerance accumulations, the boards 33, 39 may stillproperly mate within the motherboard 50 due to the extra width of thefemale contacts of the motherboard with respect to the individualcontacts 51-51 of the printed circuit boards.

FIG. 3 illustrates a sectional view taken along the lines 3-3 of FIG. 2,wherein the motherboard 50 is coupled to a second motherboard 52 bymeans of flexible wiring tape 53. The flexible wiring tape 53 fitswithin a concavity of a dummy electronic unit 54. A dummy unit 54 isinserted between each functional set of units 11. This dummy unit 54would reside between two adjacent motherboards 50, 52 which areconnected to each other by the flexible printed wiring tape 53, thelength of the flexible printed wiring tape being somewhat in excess ofthe width of the dummy unit 54. The flexible tape 53 is of sufficientlength to form a loop within the concavity, so that, due to tolerancelimitations and errors that may occur, close compacting of theelectronic units 11-11 can occur without physically damaging thecontacts 51-51 or the motherboards 50, 52.

Referring to FIGS. 3 and 4, the motherboard 50 (and, similarly, themotherboard 52) is constructed physically of two portions: an epoxycircuit board portion 50a and a rigid female connector plate 50b. Thus,the male contacts 51-51 from the electronic units 11-11 fit within thefemale connector plate 5011, the connector plate 50b providing contactsthen directly to the epoxy circuit board 50a. The epoxy circuit board50a and the connector plate 50b act as a motherboard 50 and, by thenature of its construction, combines the versatility of printedcircuitry, via the epoxy circuit board 500, together with the structuraladvantages that a rigid connector plate 50b offers. One advantage ofusing flexible wiring tape 53, such as polyethylene terephthalate tape(such tape being available under the trademark name Mylar) is to takecare ofa situation wherein each of the units 11 is not precisely tosize. The units 11 may vary in tolerance so that if the units ll-ll areslightly oversized or slightly undersized, improper fitting might occur.However, by using flexible printed wiring, the motherboards 50, 52permitted to float, all the units 11-11 can fit without jamming, and theunits 1l-11 properly mate with the motherboards 50, 52.

As illustrated in FIG. 6, the electronic unit 11 may house components34-34, which components 34, typically, may be flat packs and otherminiaturized circuits including beam lead integrated circuits and thelike, which can be affixed directly to the printed circuitry of theprinted circuit board 33. As an alternative, or in addition if it is sodesired, discrete larger components, such as a resistor 61, as shown inFIG. 7, can be held against the surface of the printed circuit board 39,with its leads 62 going through the laminate 43, the hollow spacing orchamber within the unit 11, through the laminate 36, and affixed to thecircuitry of the printed circuit board 33. In such a case, it is desiredthat the leads 62 of the resistor 61 be enclosed within the spacingbetween the two laminates 43, 36 by an insulating epoxy button 63. As afeature, the electronic unit 11, when holding discrete components, suchas resistors 61 may have the epoxy button 63 placed within the airspacing between the two opposed laminates 36, 43 which is cemented inplace with epoxy. Then, a hole is drilled through the two laminates 36,43 through the epoxy button 63 so that the resistor 61 wire lead can befed through the epoxy button 63. The button 63 isolates the resistor 61from the coolant fluid that is to be passed between the spacings of theelectronic units 11-11. The button 63, or equivalent, is necessary forcertain government requirements and is highly desired from a safetyviewpoint in that, one, a fire hazard is eliminated and, two, airleakage through the resistor hole is inhibited.

FIG. 5 is a schematic plan view showing the flow of cooling fluidthrough the system 10, wherein cooling fluid can be passed through theintake orifice 14 of the front mounting plate 13, and passed through aplenum 66 formed by the elongated apertures 28 of each of the electronicunits 11-11. The cooling fluid then passes from the plenum 66, inparallel, through all the slot portions 32a, 32b of the. electronicunits 11-11, through the hollow spacings 67-67 within the units 11-11,and out through all the slot portions 29a 29b thereof to the cavity 68formed by all of the elongated apertures 27 of the electronic units11-11. Cooling fluid, then, passes therefrom through an exiting orifice69 in the rear mounting plate 18. Thus, as illustrated in FIG. 5, airflows in directly through the front of the system 10, into the plenum66, in parallel through all the spaces 67-67 within the units 11- 11,through the cavity 68, and then out through the exiting orifice to therear of the system 10.

IN GENERAL With the rigid construction provided, the modular electronicsystem 10 is able to withstand high vibrations, high shock, and high gaccellerations making it highly suitable for use in aircraft andspacecraft. Due to its construction, it is inherently a rigid lowvibration transmissibility structure.

By using a parallel air pressure system through the spacings 67-67within the units 11-11, there is a low pressure drop from the input airto the output air, thereby maintaining the input airflow rate. A highpressure input air source, thus, is not required. Comparatively, serialconfigurations of the prior art would, typically, require 4 inches ofwater drop pressure, whereby in the novel embodiment described, only oneinch of water pressure drop is required. Air is fed through the front ofthe system 10, through the plenum 66 at the right of the electronicunits 11-11. All the units 11-11 are cramped closely together so that asingle plenum 66 is formed. The air then passes through the internalspacings 67 of the units 11-11 into the left cavity 68 which is formedby-the apertures 27-27 and out through the outlet 69 at the rear of thesystem 10.

The overall modular system 10 can be made expandable because of theindependent front mounting plate 13 and the independent rear mountingplate 18, so that if it is desired to add additional electronic units11-11, the rear plate 18 can be extended so that additional units 11-11can be inserted therein. The two clamping arms 19-19 can be replaced bylarger or longer arms.

This invention is applicable to almost any kind of electronic system,such as television, radar, computers, and the like, with especialemphasis on large industrial or government systems. For example, in adata processing system, a plurality of cards can form an input-outputunit, a processing unit, a memory, a power supply, and a voltageregulator. It is desirable that these blocks" be modular and removableand functionally independent of each other. It is desired that aninterconnection system be associated with each of the blocks."

The metal sheets 35, 41, in the preferred embodiment, are copper,although aluminum or another suitable conductive metal may be used.Copper is preferred because it is easy to manufacture. A copperinterface between the components and the air acts as a thermal diffuserto spread heat concentrations. It decreases the heat density over alarge surface of the copper sheet. The frames 20, are, preferably, hardanodized aluminum. There is some, but very little, heat dissipationthrough the frame 20. This ,is advantageous because if an air supply istemporarily terminated. then there is some heat dissipated through theframe 20 of the individual units 11-11,

and, in case ofcatastrophic failure of the air flow, heat can still bedissipated for a short period of time. This would find advantage inmissile applications or space applications where airflow may betemporarily disrupted for l or 20 minutes. During this temporary period,in missile or space flight, the heat could be dissipated through theoutside of the aircraft. This would be somewhat similar to prior artsystems wherein heat would be dissipated continuously in this manner;however, with this invention, heat would be removed only temporarilyduring that interval of failure.

CONCLUSION Various modifications will suggest themselves to thoseskilled in the art, without departing from the spirit and scope of thisinvention. For example, each individual frame 20 can be provided withgaskets about the large apertures 27, 28 to prevent leakage of air. Inaddition, this design is adaptable for continuous heat dissipation bythermal conduction by including an additional plate through which acooling fluid passes. Sandwiched between this plate and the irregularsurface formed by the plurality of frames 20 would be a thin flexiblesheet, made from a good thermally conductive material, which wouldpermit sufficient thermal conduction between the irregular surface andthe additional plate. Therefore heat is removed from the system bythermal conduction from the copper sheets, e.g., 35 and 41, through theframe 20, through the sheet of conductive material to the external coldplate the temperature of which is maintained at some approximately lowlevel by the cooling fluid.

We claim:

1. A modular electronic system comprising A. a plurality of stackedelectronic circuit units having a first cavity through the stack alongone edge thereof, and a second cavity through the stack along anopposite edge thereof, each of said units having a chamber joining saidfirst cavity to said second cavity, each of said units including, afirst insulated printed circuit board having components thereon and afirst sheet of heat conductive material forming together a firstlaminate, a second insulated printed circuit board having componentsthereon and a second sheet of heat conductive material forming togethera second laminate, and a frame holding said first laminate on one sidethereof and holding said second laminate on the opposite side thereofforming said chamber therebetween, said frame having a pair of slotsconnecting said chamber to said first cavity and to said second cavity,

B. a first mounting plate having an orifice therethrough communicatingwith said first cavity,

C. a second mounting plate having an orifice therethrough communicatingwith said second cavity, and

D. means clamping said first mounting plate, said stacked units, andsaid second mounting plate together forming a continuous passagewaythrough 1. said first mounting plate orifice, through 2. said firstcavity, through, in parallel,

a. all of said chambers, through 3. said second cavity, and exitingthrough 4. said second mounting plate orifice. 2. A modular electronicsystem comprising: A. a plurality of stacked electronic circuit units,each ofsaid units including 1. a first, substantially rectangular,printed circuit board having components thereon, 2. a first,substantially rectangular, thin sheet of heat conductive material,

3. insulating means for laminating said first printed circuit board tosaid first sheet, thus forming a first laminate, 4. a second,substantially rectangular printed circuit board having componentsthereon, 5. a second, substantially rectangular, thin sheet of heatconductive material,

6. insulating means for laminating said second printed circuit board tosaid second sheet, thus forming a second laminate,

7. a hollow, heat conductive frame holding said first laminate on oneside thereof, and holding said second laminate on the opposite sidethereof, the sheets of both of said laminates being oriented inwardlywith respect to said frame and separated from each other to form achamber between them, said frame being formed in a generally rectangularconfiguration having four border members,

a. one of said border members having a first elongated aperture formedtherethrough and therealong from one side of said frame to the oppositeside of said frame, and further having a first slot joining said firstelongated aperture to said chamber, and

b. a second of said border members, nonadjacent to said one member,having an elongated aperture hereinafter termed second elongatedaperture formed therethrough and therealong from one side of said frameto the opposite side of said frame, and further having aslot-hereinafter termed second slot-joining said second elongatedaperture to said chamber, and

8. means affixing said laminates to said frame,

B. a front mounting plate, in contact with one end of said stackedelectronic units, having an orifice therethrough communicating with thefirst elongated apertures of said frames,

C. a back mounting plate, in contact with the opposite end of saidstacked electronic units, having an orifice therethrough communicatingwith the second elongated apertures of said frames, and

D. means clamping the front and back mounting plates and theintermediately oriented stacked electronic units forming a continuouspassageway through 1. said front mounting plate orifice, through 2. aplenum formed by the stacked first elongated apertures ofsaid circuitunits, through, in parallel,

a. the first slots of all of said frames, then,

b. said chambers of all of said frames, thereby directly cooling saidsheets and indirectly cooling said boards and the components on saidboards, and then c. the second slots of all said frames,

3. a cavity formed by the stacked second elongated apertures of saidcircuit units, and exiting through 4. said backmounting plate orifice.

3. The modular electronic system as recited in claim 2 further whereinsaid printed circuit boards have male electrical contacts disposed alonga third of said border members, and further comprising electricalinterconnecting means including female electrical contacts mating withsaid male contacts.

4. The modular electronic system as recited in claim 3 wherein each maleelectrical contact has a width substantially greater than its thickness,said male contacts being so oriented with their widths perpendicular tothe surface of the printed circuit boards, and wherein the mating femaleelectrical contacts are tight fitting with respect to thickness andloose fitting with respect to width.

5. The modular electronic system as recited in claim 4 wherein saidelectrical interconnecting means comprises A. a first electricalinterconnect board containing female electrical contacts communicatingwith corresponding male contacts of a first plurality of adjacentstacked electronic circuit units;

B. a second electrical interconnect board containing female electricalcontacts communicating with corresponding male contacts of a secondplurality of adjacent stacked electronic circuit units; and

C. flexible electrical wiring tape joining said first interconnect boardto said second interconnect board, said tape having a length exceeding L+T;

said system further comprising a dummy electroniccircuit unit includinga plate having a width L having elongated apertures along two oppositeborders thereof so as to align, plenum and cavity, with the first andsecond pluralities of stacked units, said plate having a concavitywithin a third border thereof so as to receive a loop of said tapetherewithin, and wherein the value T represents the maximum dimensionaltolerance error in width that can occur by stacking a first plurality ofadjacent stacked circuit units together. 6. The modular electronicsystem as recited in claim 2 further wherein each of said stackedelectronic circuit units contains a heat conductive structural memberjoining one of

1. A modular electronic system comprising A. a plurality of stackedelectronic circuit units having a first cavity through the stack alongone edge thereof, and a second cavity through the stack along anopposite edge thereof, each of said units having a chamber joining saidfirst cavity to said second cavity, each of said units including, afirst insulated printed circuit board having components thereon and afirst sheet of heat conductive material forming together a firstlaminate, a second insulated printed circuit board having componentsthereon and a second sheet of heat conductive material forming togethera second laminate, and a frame holding said first laminate on one sidethereof and holding said second laminate on the opposite side thereofforming said chamber therebetween, said frame having a pair of slotsconnecting said chamber to said first cavity and to said second cavity,B. a first mounting plate having an orifice therethrough communicatingwith said first cavity, C. a second mounting plate having an orificetherethrough communicating with said second cavity, and D. meansclamping said first mounting plate, said stacked units, and said secondmounting plate together forming a continuous passageway through
 1. saidfirst mounting plate orifice, through
 2. said first cavity, through, inparallel, a. all of said chambers, through
 3. said second cavity, andexiting through
 4. said second mounting plate orifice.
 2. said firstcavity, through, in parallel, a. all of said chambers, through
 2. Amodular electronic system comprising: A. a plurality of stackedelectronic circuit units, each of said units including
 2. a first,substantially rectangular, thin sheet of heat conductive material,
 2. aplenum formed by the stacked first elongated apertures of said circuitunits, through, in parallel, a. the first slots of all of said frames,then, b. said chambers of all of said frames, thereby directly coolingsaid sheets and indirectly cooling said boards and the components onsaid boards, and then c. the second slots of all said frames,
 3. acavity formed by the stacked second elongated apertures of said circuitunits, and exiting through
 3. insulating means for laminating said firstprinted circuit board to said first sheet, thus forming a firstlaminate,
 3. said second cavity, and exiting through
 3. The modularelectronic system as recited in claim 2 further wherein said printedcircuit boards have male electrical contacts disposed along a third ofsaid border members, and further comprising electrical interconnectingmeans including female electrical contacts mating with said malecontacts.
 4. The modular electronic system as recited in claim 3 whereineach male electrical contact has a width substantially greater than itsthickness, said male contacts being so oriented with their widthsperpendicular to the surface of the printed circuit boards, and whereinthe mating female electrical contacts are tight fitting with respect tothickness and loose fitting with respect to width.
 4. said secondmounting plate orifice.
 4. a second, substantially rectangular printedcircuit board having components thereon,
 4. said back mounting plateorifice.
 5. a second, substantially rectangular, thin sheet of heatconductive material,
 5. The modular electronic system as recited inclaim 4 wherein said electrical interconnecting means comprises A. afirst electrical interconnect board containing female electricalcontacts communicating with corresponding male contacts of a firstplurality of adjacent stacked electronic circuit units; B. a secondelectrical interconnect board containing female electrical contactscommunicating with corresponding male contacts of a second plurality ofadjacent stacked electronic circuit units; and C. flexible electricalwiring tape joining said first interconnect board to said secondinterconnect board, said tape having a length exceeding L +T; saidsystem further comprising a dummy electronic circuit unit including aplate having a width L having elongated apertures along two oppositeborders thereof so as to align, plenum and cavity, with the first andsecond pluralities of stacked units, said plate having a concavitywithin a third border thereof so as to receive a loop of said tapetherewithin, and wherein the value T represents the maximum dimensionaltolerance error in width that can occur by stacking a first plurality ofadjacent stacked circuit units together.
 6. The modular electronicsystem as recited in claim 2 further wherein each of said stackedelectronic circuit units contains a heat conductive structural memberjoining one of said border members intermediate said first elongatedaperture to the second of said border members intermediate said secondelongated aperture forming chamber portions, the width of the variousstructural members being optimized so as to vary the cross-sectionalarea of the chamber portions of each unit, so as to optimize the degreeof cooling of each circuit unit.
 6. insulating means for laminating saidsecond printed circuit board to said second sheet, thus forming a secondlaminate,
 7. a hollow, heat conductive frame holding said first laminateon one side thereof, and holding said second laminate on the oppositeside thereof, the sheets of both of said laminates being orientedinwardly with respect to said frame and separated from each other toform a chamber between them, said frame being formed in a generallyrectangular configuration having four border members, a. one of saidborder members having a first elongated aperture formed therethrough andtherealong from one side of said frame to the opposite side of saidframe, and further having a first slot joining said first elongatedaperture to said chamber, and b. a second of said border members,nonadjacent to said one member, having an elongated aperture-hereinaftertermed second elongated aperture-formed therethrough and therealong fromone side of said frame to the opposite side of said frame, and furtherhaving a slot- hereinafter termed second slot-joining said secondelongated aperture to said chamber, and
 7. The modular electronic systemas recited in claim 2 wherein said front mounting plate and said backmounting plate are constructed of heat conductive material.
 8. meansaffixing said laminates to said frame, B. a front mounting plate, incontact with one end of said stacked electronic units, having an orificetherethrough communicating with the first elongated apertures of saidframes, C. a back mounting plate, in contact with the opposite end ofsaid stacked electronic units, having an orifice therethroughcommunicating with the second elongated apertures of said frames, and D.means clamping the front and back mounting plates and the intermediatelyoriented stackEd electronic units forming a continuous passagewaythrough